1. Field of the Invention
The present invention relates to a magnetic transducer head utilizing the magnetoresistance effect.
2. Prior Art
FIGS. 1 and 2 are a magnified plan view and magnified cross-sectional view, respectively, showing the principal portion of the magnetic head utilizing the magnetoresistance effect. This magnetic head has a magnetoresistance element located rearwardly offset with respect to the contact plane confronting the magnetic recording medium, and is categorized as a so-called rear-type magnetic head. The structure of the rear-type magnetic head is as follows. On a magnetic substrate 1 made of, for example, Ni-Zn ferrite or Mn-Zn ferrite, there is deposited through an insulating layer 2 of SiO.sub.2, Si.sub.3 N.sub.4, etc., if the substrate 1 is conductive such as the case of Mn-Zn ferrite, a current means 3 in the form of a band of conductive layer for producing a bias magnetic field for a magnetoresistance element, as will be described later, by being supplied by a conditioning currrent supply means B, FIG. 1, a bias current. The current means 3 is overlaid through an insulating layer 4 similar to the layer 2 by a magnetoresistance element 5 made of, for example, Ni-Fe alloy or Ni-Co alloy film measuring, for example, 10 m width and 300-500 A thick. The magnetoresistance element 5 is overlaid by a similar insulating layer 6, on which magnetic layers 7 and 8 made of, for example, Ni-Fe alloy in a thickness of about 7000 A are formed so as to construct a magnetic circuit extending across the magnetoresistance element 5 and current means 3. The front end of the magnetic layer 7 extends over the substrate 1 through a non-magnetic gap spacer 9 in a thickness of, for example, 3000 A, and a magnetic gap g, with its gap length defined by the thickness of the gap spacer 9 between the magnetic layer 7 and substrate 1, is formed in the contact plane 10 confronting the magnetic recording medium. The rear end of the magnetic layer 8 is terminated on the substrate 1, for example, in direct contact with each other, so that both members magnetically couple tightly. The rear end of the magnetic layer 7 and the front end of the magnetic layer 8 confront each other with a spacing W provided therebetween, so that a discontinuous section or discontinuity region 11 of the magnetic circuit is formed, and the magnetic circuit is closed magnetically by placing the magnetoresistance element 5 in the discontinuous section 11. Accordingly, the rear end of the magnetic layer 7 and the front end of the magnetic layer 8 are placed on the magnetoresistance element 5 through the insulating layer 6, and the insulating layer 6 is made thin so that the magnetoresistance element 5 is magnetically coupled with both end sections. Thus, a closed magnetic circuit from the substrate 1 to the magnetic gap g, magnetic layer 7, magnetoresistance element 5, magnetic layer 8, and back to the substrate 1 is formed.
A magnetic head element h provided with the magnetic gap g and magnetoresistance element 5 within the magnetic circuit on the substrate 1 is now completed. For a multi-channel magnetic head, magnetic head elements h each constructed as described above are arrayed in parallel on the common substrate 1.
In practice, the magnetic head element h formed on the substrate 1 is covered by a non-magnetic protection layer 12, which is joined to a protection plate 14 by an adhesive layer 13 to complete a magnetic head.
The magnetic head constructed as described above operates as follows. The magnetic flux carrying a signal produced by the magnetic recording medium confronting the contact plane 10 is conducted through the gap g to the magnetoresistance element 5 within the magnetic circuit so that the signal is detected by sensing the variation of resistance. For this purpose, i.e., in order to produce an output or readout representative of the variation of resistance, a sense current is supplied by a source S to the magnetoresistance element 5. In order for the magnetoresistance element to have high sensitivity and linearity, it is given a certain amount of bias magnetic field by application of a current (will be termed "bias current") to the current means 3.
The current means 3 providing a bias magnetic field for the magnetoresistance element has the output characteristics as shown in FIG. 3, in which in a state of the magnetoresistance element supplied with a certain sense current the output increases linearly as shown by the solid curve a until the input bias current i.sub.B reaches a certain value i.sub.Bo. Accordingly, the magnetic head of this type is used for reproduction of a record on the magnetic recording medium by application of a bias current I.sub.B around the value i.sub.Bo to the current means. In actuality, however, the magnetic circuit including the substrate 1, magnetic layers 7 and 8, and magnetoresistance element 5 has a property of hysteresis, and the output characteristics exhibit the hysteresis as shown by the dashed curve b in FIG. 3. Namely, the previous state of the magnetic head affects the output characteristics of the next playback or readout operation to produce a different output for the same bias current I.sub.B, resulting in an unstable output of the magnetic head. This is particularly undesirable for a multi-channel magnetic head having a plurality of magnetic head elements h, in which the hysteresis of each head element causes disparity of outputs among channels. In addition, the application of a bias current I.sub.B around i.sub.Bo at the beginning of the playback operation causes the creation of an unstable magnetic domain wall, which possibly causes the generation the Barkhausen noise.